Charly,
It might sound like these guys are suggesting a backyard fix, but on page 35 of the owners manual, it does say to use "...liquid wrench or similar penetrating
oil/lubricant" on the suspension bushings. I give 'em all a little squirt every time I have the car up for greasing and service. If that's not it, you may have to use Dan's toilet tank washer trick. Please let us know what you find.